What was the sole purpose for Phillis Wheatley's poems?

A poet's motivations are always challenging.  One can argue that a driving purpose of Wheatley's work and life was to transform what is into what can be.  Being an African slave, she defied the conventions of what is and demonstrated that literacy can be the doorway to the greatest of voices.  In highlighting what can be, she wrote in Classical Elegiac style.  Purchasing her own freedom, she wrote in ardent support of the American Revolution, a moment in time that identified what is and moved it into the domain of what can be.  Finally, in speaking out about the American institution of slavery, she articulated a vision of national identity that was divergent from the Status Quo.  These transformative notions could have served as the basis for her poetry.